Aphanizomenon has a filamentous thallus, which can either exist as free-floating and isolated filaments or come together to create colonies. These colonies exhibit a distinct parallel arrangement, resembling clumps of grass clippings floating on the water’s surface. The cells within Aphanizomenon are typically cylindrical or barrel-shaped and have a pale blue-green coloration. All species in this genus are planktonic, capable of forming dense blooms, and can produce saxitoxins, which are associated with certain toxins.